As our ancestors evolved verbal communication, we can imagine that one of their earliest sounds eventually gave rise to the Proto-Indo-European labiovelar */kw/. This became /hw/ in Proto-Germanic, wh in English and qu in Latin. In a wholly inscrutable world to their emerging consciousness, short, rudimentary expressions of wonder must have been the most common. Over time, they turned into English wh-words: what, who, where, when, and Latin qu-words: quid, quis, quo, quando.

Although we are the only species able to verbalise them, other animals are evidently aware of identification, spatial location and temporal sequence. We don’t know what it is like to be a bat, but – pace Thomas Nagel – it is not difficult to imagine that a bat must have some sense of what (an insect, an eagle, a cave, another bat), very much a sense of where, and also a sense of when, at least in the basic forms of now and later, and possibly before. The closer the animal is to us, the easier it is for us to empathise: simpler with a cat, harder with a rat, near impossible with a gnat, or a brain in a vat.

But there is one wh-word that makes no sense to any other animal: why. When a bat eats an insect, or is eaten by an eagle, it has a sense of what happened, where and when, but not of why. Only humans know why something happened: it is be-cause – what caused it to be.

Answering why is to explain, i.e. to make plain, to unfold. As such, it is a verbal act, impossible without a well-articulated language. Parents know: at one point, children start bombarding them with why questions. But not immediately. Until they develop enough vocabulary, children don’t ask why. Rather, they are interested in knowing what happens if. This is the same question they have learnt to answer by themselves since birth. By the time they start talking, children already know what happens if, for example, they release an object from the grasp of their hands. They know that the object always does more or less the same thing: it falls down – rather than e.g. float in the air, fly out of the window or disappear. They have learnt this by experience, which literally means getting over the peril of the unknown. Just like a cat, a baby has no idea of why an object falls to the ground, but he knows that it does – unfailingly and, therefore, predictably – through the hard evidence of repeated experiment.

Language gives children the opportunity to learn not just from their own experience, but also from the experience of others, and not just by observing what others do, but by listening to, and trusting, what they say. So, for example, to learn what happens if they put a finger on a flame they no longer need to try themselves the hard way: they can ask their dad, and trust that, if dad says it happens that way, that’s the way it always happens. It is through such extension of experience from hard to soft evidence that parents introduce their children to the wonderful world of why. Once they not only tell them what happens if they put a finger on a flame, but explain to them why it happens, they have opened the floodgates:

You can’t do it because the flame will burn your finger. Why? Because fire is very hot and your nerves will send a message to the brain to retract the hand. Why? Because otherwise your finger will burn. Why? Because it can only bear a certain temperature. Why?

As every parent knows, the dreaded why-chain has only a few rings, before ending abruptly in a more or less emotional …because that’s the way it is!

Each ring is a cause, explaining a fold in the tangle of reality. Children would never stop unfolding: no ring looks like the last to them. So they keep asking, under the reasonable expectation that grownups must have surely figured everything out. The realisation that they haven’t – that in the end no one really knows – is a critical stage in children’s development, roughly coinciding with the acquired awareness of another nasty surprise: death. It is through sombre resignation that children stop asking why and learn to accept local explanations. As in:

Why do I have to brush my teeth every day? Because otherwise you get caries. Wh-… All right, fine, whatever.

By that time, parents have ceased to be the exclusive source of soft evidence. As children extend their social reach – go to school, make friends – more and more of what they know is because somebody else said it, they trust it to be true and get on with it.

As adults, most of what we know results from the accumulation of trusted soft evidence. This sets us apart from other animals. They only know by hard evidence and imitation. We know – incomparably more – by soft evidence and trust.